Sniper's high burst damage is useful in the early-game and mid-game. Use it to pop high-HP Bloons, especially the Blooming Bloon. Notably, it can one-shot a Blooming Bloon except if buffed by the passives of Amelia or Zee Jay. It has greater damage-to-gold ratio to single targets than most early-game Monkeys.
Compared to the Bomb Shooter, which costs 1 less Gold and has Armor Piercing, the Sniper has one less reload, has 10 extra ATK, and counts as a Military Monkey (mainly impactful for War Bonds).
Night Vision Sniper costs 1 Gold more with 10 extra ATK than the normal Sniper. In Striker Jones decks, having both of these Snipers is useful to survive early-game more consistently.
Sniper is a good candidate as an early-game Try This! synergizer. Although other early game monkeys are more common, Sniper is a decent choice for an early game monkey, having high DPT for his cost and dealing a good amount of burst damage.
Sniper can be used by Ezili as a good target for Totem.